Metal-organic frameworks incorporating azobenzene-based ligands as a heterogeneous Lewis-acid catalyst for cyanosilylation of imines

In this work, two novel metal-organic frameworks (MOFs) were synthesized by the reaction of azobenzene-based ligands and Zn(NO3)(2)/CdCO3 under solvothermal conditions with the formula of {[Zn-2(abtc)(azpy)(H2O)(2)]center dot 4H(2)O}(n) (1) and {[Cd(abtc)(0.5)(azpy)(0.5)(H2O)]center dot 3H(2)O}(n) (2) (H(4)abtc = 3,3',5,5'-azobenzene tetracarboxylic acid, azpy = 4,4'-azobipyridine). According to the single-crystal X-ray diffraction (SC-XRD) analysis, complexes 1 and 2 possessed quite similar structures except for the coordination modes of the central metal nodes attributed to the difference between the cationic radius of Zn(II) and Cd(II). The Zn(II) cations in 1 adopted a distorted seesaw coordination geometry and the coordination between Zn(II) and organic linkers gave two-dimensional (2D) coordination networks, while the Cd(II) cations in 2 could also bind with the carboxylate groups from neighboring coordination networks to form a three-dimensional (3D) coordination framework. Furthermore, complexes 1 and 2 showed high catalytic activity as heterogeneous Lewis-acid catalysts towards the cyanosilylation of imines with satisfactory reusability under mild conditions and the similar catalytic performance of 1 and 2 could be attributed to the similarity in their structures. A prudent mechanism has been proposed as well to elucidate the role of complexes 1 and 2 in the catalytic process.

Automated summary

In this study, two novel metal-organic frameworks (MOFs) were synthesized and their structures were analyzed. These complexes exhibited high catalytic activity and satisfactory reusability under mild conditions. These findings are significant for the application and catalytic field of MOFs.